Method and device for driving a gas discharge lamp

Abstract

A driver ( 1 ) for driving a gas discharge lamp ( 2 ) comprises:—a current source ( 3 ) generating lamp current, having a setpoint input ( 4 ) for receiving a setpoint signal;—a controller ( 10 ) generating a current setpoint signal (SM);—a controllable noise signal source ( 20 ) generating a pseudo random noise signal (SPRNS);—an adder ( 22 ) adding the current setpoint signal (SM) from the controller and the pseudo random noise signal (SPRNS) from the noise signal source, and providing the result to the setpoint input of the current source;—measuring means ( 40 ) measuring a characteristic lamp response of the lamp in response to the pseudo random noise signal (SPRNS), and providing to the controller a sense signal;—a memory ( 30 ) associated with the controller, having stored therein at least one reference signal. The controller compares the measured lamp response with said predetermined reference signal in the memory, and may switch off the lamp.

1. Driver ( 1 ) for driving a gas discharge lamp ( 2 ), comprising:
 a current source ( 3 ) for generating lamp current, having a setpoint input ( 4 ) for receiving a setpoint signal; 
 a controller ( 10 ) having an output ( 12 ) for generating a current setpoint signal (S M ); 
 a controllable noise signal source ( 20 ) controlled by the controller ( 10 ), designed for-generating a pseudo random noise signal (S PRNS ); 
 an adder ( 22 ) connected to receive the current setpoint signal (S M ) from the controller ( 10 ) and the pseudo random noise signal (S PRNS ) from the noise signal source ( 20 ), and having an output coupled to the setpoint input ( 4 ) of the current source ( 3 ); 
 measuring means ( 40 ) for measuring a characteristic lamp response of the lamp ( 2 ) in response to the pseudo random noise signal (S PRNS ), coupled to a sense input ( 14 ) of the controller ( 10 ) for providing to the controller ( 10 ) a sense signal representing the characteristic lamp response; 
 a memory ( 30 ) associated with the controller ( 10 ), having stored therein at least one reference signal; 
 
       wherein the controller ( 10 ) is designed to compare the characteristic lamp response as measured by the measuring means ( 40 ) with said predetermined reference signal in the memory ( 30 ). 
     
     
       2. Driver according to  claim 1 , wherein the measuring means ( 40 ) comprises a current sensor for measuring lamp current. 
     
     
       3. Driver according to  claim 1 , wherein the measuring means ( 40 ) comprises a voltage sensor for measuring lamp voltage. 
     
     
       4. Driver according to  claim 1 , wherein the pseudo random noise signal (S PRNS ) contains, for one lamp current period, a series of subsequent current pulses, wherein the number of current pulses in said series is at least equal to 2 or more, preferably in the range from 10 to 50, most preferably in the order of about 30. 
     
     
       5. Driver according to  claim 1 , wherein the noise signal source ( 20 ) is controlled by the controller ( 10 ) for generating the pseudo random noise signal (S PRNS ) in synchronization with the current setpoint signal (S M ), such that, for different current periods, the corresponding pseudo random noise signals (S PRNS ) are mutually equal. 
     
     
       6. Driver according to  claim 5 , wherein the controller ( 10 ) is designed to average the lamp response over a plurality of lamp current periods, said plurality preferably comprising in the order of about 10 current periods. 
     
     
       7. Driver according to  claim 1 , wherein the controller ( 10 ) is designed, if the results of said comparison indicate that the lamp ( 2 ) approaches the end of its lifetime, to generate an end-of-life indication signal. 
     
     
       8. Driver according to  claim 1 , wherein the controller ( 10 ) is designed, if the results of said comparison indicate that the lamp ( 2 ) approaches the end of its lifetime, to switch off the lamp ( 2 ). 
     
     
       9. Driver according to  claim 1 , wherein the controller ( 10 ) is designed, on the basis of the results of said comparison, to adapt at least one control parameter. 
     
     
       10. Driver according to  claim 9 , wherein said control parameter to be adapted includes the steady-state current magnitude and/or the steady-state current waveform. 
     
     
       11. Driver according to  claim 1 , wherein the controller ( 10 ) is designed, on the basis of the results of said comparison, to generate a lamp type indication signal. 
     
     
       12. Driver according to  claim 1 , wherein the controller ( 10 ) is designed to switch on the noise signal source ( 20 ) after replacement of a lamp, and/or regularly at intervals corresponding to a predetermined duration of operative life, for instance every 100 hours of lamp operation.